NASA finds ice on a planet -- and it's not Mars

By SCOTT SUNDE, SEATTLEPI.COM STAFF

Updated 12:56 pm, Thursday, November 29, 2012

Photo: Associated Press

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This photo made available by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington on Tuesday, Nov. 27, 2012 shows a 68-mile-diameter crater, large indentation at center, in the north polar region of Mercury which has been shown to harbor water ice, thanks to measurements by the Messenger spacecraft. Scientists made the announcement Thursday. (AP Photo/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

This photo made available by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington on Tuesday, Nov. 27, 2012 shows a 68-mile-diameter crater, large indentation at center,

Tradar image of Mercury's north polar region f is shown superposed on a mosaic of MESSENGER images of the same area. All of the larger polar deposits are located on the floors or walls of impact craters. Deposits farther from the pole are seen to be concentrated on the north-facing sides of craters. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory

Tradar image of Mercury's north polar region f is shown superposed on a mosaic of MESSENGER images of the same area. All of the larger polar deposits are located on the floors or walls of impact craters.

Shown in red are areas of Mercury’s north polar region that are in shadow in all images acquired by MESSENGER to date. Image coverage, and mapping of shadows, is incomplete near the pole. The polar deposits imaged by Earth-based radar are in yellow and the background image is the mosaic of MESSENGER images. This comparison indicates that all of the polar deposits imaged by Earth-based radar are located in areas of persistent shadow as documented by MESSENGER images. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory

Shown in red are areas of Mercury’s north polar region that are in shadow in all images acquired by MESSENGER to date. Image coverage, and mapping of shadows, is incomplete near the pole. The polar deposits

But that's crazy, right? How could there be ice on the closest planet to the sun? It turns out the deep craters shade anything inside from the sun's rays, keeping the temperature cool enough to allow ice to form. It's even possible that liquid water exists on the planet somewhere under the ice!

NASA reports:

New observations by the MESSENGER spacecraft provide compelling support for the long-held hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed polar craters.

Three independent lines of evidence support this conclusion: the first measurements of excess hydrogen at Mercury's north pole with MESSENGER's Neutron Spectrometer, the first measurements of the reflectance of Mercury's polar deposits at near-infrared wavelengths with the Mercury Laser Altimeter (MLA), and the first detailed models of the surface and near-surface temperatures of Mercury's north polar regions that utilize the actual topography of Mercury's surface measured by the MLA. These findings are presented in three papers published online today in Science Express.

MESSENGER -- the name stands for "Mecurity Survce, Space Environment, Geochemistry and Ranging" -- is a robotic spacecrafit and the first ever to orbit Mercury

It arrived last year and its findings, NASA says, "are consistent with the water-ice hypothesis."

Now the newest data from MESSENGER strongly indicate that water ice is the major constituent of Mercury's north polar deposits, that ice is exposed at the surface in the coldest of those deposits, but that the ice is buried beneath an unusually dark material across most of the deposits, areas where temperatures are a bit too warm for ice to be stable at the surface itself.

We're talking lots of ice. The New York Times reports that Mercury may have 100 billion to 1 trillion tons, enough to encase Washington, D.C., 2 1/2 miles deep.

Scientists think the dark material could be a mix of complex organic compounds that comets and asteroids brought to the planet.

That stuff adds a "new wrinkle" to the story, NASA quotes Sean Solomon of the Columbia University's Lamont-Doherty Earth Observatory, principal investigator of the MESSENGER mission, as saying

"For more than 20 years the jury has been deliberating on whether the planet closest to the Sun hosts abundant water ice in its permanently shadowed polar regions. MESSENGER has now supplied a unanimous affirmative verdict.

"But the new observations have also raised new questions," adds Solomon. "Do the dark materials in the polar deposits consist mostly of organic compounds? What kind of chemical reactions has that material experienced? Are there any regions on or within Mercury that might have both liquid water and organic compounds? Only with the continued exploration of Mercury can we hope to make progress on these new questions."